1. Field of the Invention
The present invention relates to nuclear qualified in-containment electrical connectors and methods of connecting electrical conductors for use in electrical connections of thermocouples and instrumentation in the environment within the containment of a nuclear power plant.
2. Description of the Prior Art
It has become known that many commercial nuclear power plants were operating with nuclear safety related instrumentation for which there was no documentation showing that the instrumentation would function in the event of a nuclear accident and the resultant exposure of the instrumentation to the environment produced by such a nuclear accident. This problem has become better known as a result of commercial nuclear power plant accidents which have occurred when the industry, government, and public became aware that a reactor melt down was possible and that nuclear environmentally qualified instrumentation was an absolute necessity in order to avoid a disaster. Government regulatory bodies over the last few years has exerted great pressure on operating utilities to demonstrate and document that nuclear safety related instrumentation would function when required under the high temperature, pressure, steam and radiation conditions resulting from a nuclear accident. This has resulted in costly instrument redesign and nuclear environmental qualification test programs by instrument vendors, power plant design agencies, and utilities which have taken years to complete. Such qualification programs have often met with frustration when instruments failed the qualification testing and required design changes and repetition of lengthy and costly qualification programs. One of the common problems affecting the qualification programs was the inability to seal the electrical wires entering the instrument. Failure of this seal results in moisture and chemicals entering the instrument resulting in instrument failure.
Development programs have been reported on the effects of aging on the performance and reliability of equipment, including environmental testing such as accident dose irradiation testing of an in-containment portion of a pressure transmitter system utilizing an electro-mechanical transducer which failed, the cause of failure being subsequently determined to be shorting of the turns inside the coils due to ingress of chemical laden moisture. It was found that under 66 psig steam pressure, water had entered cracks in the pigtail insulation and had migrated down the wire stranding into the sealed area between the core plug and the core, and migrated by capillary action up the stranded leads and into the coil where it shorted the coil windings causing the unit to fail. "CE In-Containment Nuclear Pressure Transmitter: A Qualification Status Report", TIS-7330, by K. A. Martin, J. S. Dietrich, A. A. Oja, and C. R. Musick, Nuclear Power Systems, Combustion Engineering, Inc., Windsor, Conn., presented at the Nuclear Power Systems Symposium, Oct. 22, 1982, Washington, D.C.
Other types of electric conductor seal assemblies for in-containment applications for normal and abnormal conditions including seismic and loss of coolant accident (LOCA) design basis events are known from Conax Corporation Bulletin SA 1000, "Conax Electric Conductor Seal Assemblies", Conax Corporation, Buffalo, N.Y. Conax Corp. also provides a commercially available feed through connector shown in a catalog and entitled "Insulated Lead Sealing with Conax PL Glands for use including nuclear applications".
The use of heat shrinkable tubing, or dimensionally recoverable sleeves, in electrical connector assemblies is also known from U.S. Pat. No. 4,518,819, U.S. Pat. No. 4,464,540, U.S. Pat No. 4,487,994 and U.S. Pat. No. 3,984,912 for example.